Europa: Thin Ice and Contamination

by Paul Gilster on April 12, 2011

These days funding for missions to some of the most interesting places in the Solar System is much in question. But sooner or later we’re going into the outer system to investigate the possibilities for life on worlds like Europa, Enceladus or Titan. The case for Europa seems particularly compelling, but we have to be careful about our assumptions. When the Europa Orbiter Science Definition Team developed a strategy for Europan exploration in 1999, it was generally believed that any Europan ocean would be covered by a thick and impermeable layer of ice. Life, then, might exist around deep sub-oceanic volcanic vents if it existed at all.

Thus the strategy for Europan exploration that evolved: Three missions, beginning with an orbiter, followed up by a lander and, finally, a third mission that would drill down through the presumably many kilometers of surface ice to explore whatever lay beneath. Even in more financially optimistic times, that strategy didn’t get us into Europa’s ocean until well after 2030, and today we struggle to come up with a date for the Europa Jupiter System Mission (surely later than 2030 just for an orbiter), with a timetable for ocean exploration that is without doubt set back by decades.

Re-examining Europan Exploration

Why not then, says Richard Greenberg, take time to re-evaluate our entire Europan strategy, factoring in all the work that has been done sine the late 1990s? Greenberg (Lunar and Planetary Laboratory, University of Arizona) is the author of Unmasking Europa (Springer, 2008), which sharply critiques the ‘thick ice’ assumption by pointing to many instances of Galileo imagery showing what appears to be young and constantly resurfacing ice. Cracking and melting of a thinner ice sheet could actually expose the ocean, and make the job of studying it far easier, while demanding considerable caution in terms of possible contamination from terrestrial organisms.

Image: A representation of possible subsurface structures, prepared by the Jet Propulsion Laboratory for the recent Europa Orbiter Science Definition Team (SDT-2010), shows a very different picture from the version of a decade earlier. According to SDT-2010, ‘‘The NASA Jupiter Europa Orbiter will address the fundamental issue of whether Europa’s ice shell is ~few km (left) or >30 km (right), with different implications for processes and habitability.’’ The thick ice as shown on the right extends tens of kilometers down toward the rocky interior. The model with thinner, permeable ice is now considered on par with the earlier canonical model of thick, impermeable ice. Credit: Richard Greenberg/Astrobiology.

In a new paper, Greenberg notes that the recent Joint Jupiter Science Definition Team identified the thick vs. thin ice question in 2010 as a key objective of Europa exploration. The thick ice model, in other words, is no longer the only game in town, raising real questions about how we proceed in long-term planning. Greenberg reviews the case for thin ice, especially in places like Conamara Chaos, where rafts of displaced crust can be seen lodged in what appears to be lumpy, refrozen ice, with new cracks changing the terrain yet again and suggesting melt-through. Unmasking Europa has that story in detail, but the paper offers a helpful summary to get you up to speed.

I think Greenberg’s case is strong, but I want to focus on the implications of thin ice rather than the case for it. For if we do determine that the Europan ocean is accessible, our mission focus shifts to exploiting the terrain to find the best place for surface operations. From the paper:

Rather than focusing on the daunting, perhaps impossible, task of drilling down to the ocean, we should consider how to take advantage of the biosphere’s natural accessibility. With the rapid resurfacing, almost any europan landing site might provide oceanic samples; the issue will be how to find the freshest ones. When chaotic terrain forms, it replaces a section of crust with frozen ocean. Ridge formation squeezes out ocean material. Fresh oceanic material may be exposed at the surface as gaps open up and create the dilational bands. Any of these processes could be laying out biological samples on the surface.

Thus the need, says Greenberg, to ‘land smart,’ picking the optimum landing site to avoid the need for drilling through the ice in the first place. Reassessing a Europa orbiter, then, should involve a key objective: Identifying the most likely sites where the underlying ocean may have been recently exposed. A lander integrated with the orbiter mission would have the chance of finding extraterrestrial life near or even on the surface, as the frozen remnants of materials that have been briefly exposed through surface shifting of the ice. Greenberg thinks such a strategy could give us an answer on Europan life within the lifetime of many adults living today, as opposed to pursuing what is essentially a holding strategy as we develop a thick ice drilling model.

Ice and Contamination

An overriding concern is protecting Europa from life that has hitched a ride from Earth, a problem that looms large with the thin ice model, whereas with thick ice and an isolated ocean, the chances of contamination seemed more remote. The NRC Task Group on the Forward Contamination of Europa (2000) adopted a standard for protection that says the probability of contaminating a Europan ocean with a viable terrestrial organism must be less than 10-4 per mission, referencing a 1964 resolution that Carl Sagan had a hand in fashioning with regard to the exploration of Mars.

But the Sagan formulation, developed with Sidney Coleman, is deeply flawed. Here is part of Greenberg’s critique:

The basis of the calculation was that the probability of contaminating Mars during these missions should be very small for at least the duration of the specific envisioned exploration campaign. In other words, the underlying premise of that study was that the purpose of planetary protection was to protect the interests of then currently active scientists, rather than future generations of scientists or of alien organisms themselves. They arbitrarily selected a value of 0.1% as the maximum acceptable probability of contamination. On that basis, they calculated that each spacecraft launched to Mars had to be sterilized enough so that there was less than a 0.01% chance of having any organism on board. This calculation depended on specific assumptions about unknown conditions relevant to Mars and on guesses about the future exploration program.

The international Committee on Space Research (COSPAR) accepted the Sagan/Coleman recommendation in 1964, even though its selection of a level of underlying risk was arbitrary and relied on assumptions about the survival of terrestrial organisms in space that were, in Greenberg’s view, crude. Its ethical premises were also shaky, with the assumption that we need to preserve a biosphere only long enough for the current scientific community to finish exploration. What about future generations of researchers, and what about extraterrestrial life forms themselves? This COSPAR resolution was a key source for the 2000 NRC task group report on Europa at a time when a thick ice model featuring an isolated ocean was still favored.

We need to reconsider such questions, and thankfully, a new National Research Council study on planetary protection has been commissioned by NASA, although at the moment its mission is to develop contamination standards for icy moons that are still based on Sagan/Coleman. Thus Greenberg’s call for a new analysis. And the scientist has an interesting suggestion involving what he has previously called a ‘natural contamination standard.’ It goes like this:

…exploration would be acceptable if the probability of humans infecting other planets with terrestrial microbes is smaller than the probability that interplanetary contamination happens naturally. Such a foundation principle would be ethically defensible and could be translated into specific, research-based, quantitative standards.

Greenberg also thinks the NRC panel should come up with practical sterilization criteria so that NASA can draw on an independent analysis as the basis of building Europan exploration craft. The NRC 2000 report left such matters in the hands of NASA and its contractors. The questions this raises are too significant to go unanswered. If Europa does have permeable ice, there is a distinct possibility that its biosphere extends near to the surface, raising the odds for contamination. This calls for a new look at planetary protection whatever the time frame involved, and a tightening of standards that need to move beyond those of Sagan/Coleman.

The Greenberg formulation, based as it is on a natural contamination standard, would depend on the rate of spacecraft arrivals on Europa because it would be keyed to the natural rate of interplanetary transport. It is, at least, one way of looking at contamination that takes in current data, which include the distinct possibility that we are dealing with thin and permeable ice on the distant moon. And there is a philosophical issue that trumps the proceedings. Do we have an ethical imperative to protect indigenous life forms from contamination wherever we go in the universe, and should this imperative be factored in to every mission concept we create?

If so, we need to think long and hard about the potential for thin ice on Europa, because getting the contamination question wrong would compromise both our scientific and moral objectives. The paper is Greenberg, “Exploration and Protection of Europa’s Biosphere: Implications of Permeable Ice,” Astrobiology Vol. 11, No. 2 (2011). Abstract available.

Eliminating contamination at Europa should be relatively easy – wave the drill/sampling device around for a few hours and let the radiation in the environment (from Jupiter) finish off any hardy Earth bugs.

Have any studies been done of how easy it is to detect oceanic life in/on Earth ice? If the oceans of Europa were as teeming as those on Earth, what should we expect on the surface ice — Europan salmon? Europan krill? Europan bacteria? If we landed a probe on a penguin-less Antarctic ice shelf, would the surface actually show any evidence of the ocean life underneath?

And, following from FrankH’s comment, would any organic material even survive the surface environment, or would it be broken down very rapidly by the radiation? How “fresh” would a sample have to be to show possible organics?

“Do we have an ethical imperative to protect indigenous life forms from contamination wherever we go in the universe, and should this imperative be factored in to every mission concept we create?”

There are many places on Earth that I go. It’s a place in the universe. I try to protect indigenous life forms to a reasonable extent. (AKA not waving around super viruses or wielding a flame thrower.) So then I think we’re really asking what is reasonable. This is probably the level Carl Sagan was working at. It’s not reasonable to protect Mars from every possible organism forever. It is reasonable to protect Mars while experiments are ran to determine if there is a reason to protect Mars.

I have bought into the hypothesis that you don’t have to visit planets to detect life. There is a high probability that life will use and alter the chemistry of its environment. Anyone having the ability to analyze earth’s atmosphere will instantly know there is life here.

Perhaps we have an ethical imperative to deliberately spread the biology of Earth to Europa or elsewhere. This could be done after initially testing with a good degree of certainty any planet or moon in question is indeed lifeless.

” If the oceans of Europa were as teeming as those on Earth, what should we expect on the surface ice — Europan salmon? Europan krill? Europan bacteria?”

On current evidence it seems likely that Earth life evolved multicellularity uncountably many times back in the days before photosynthesis and oxygen turned up. It was only when the oxygen atmosphere was in place and usable as a resource that multicellular life became successful enough to be a genuine long term survival advantage.

If Greenberg is correct that “With the rapid resurfacing, almost any europan landing site might provide oceanic samples…”, then perhaps a lander with roving capability (as opposed to a fixed-position lander, or the more complex ice-penetrating lander) would be the best approach to finding biological material on Europa. First, it would be much simpler than boring a hole through the ice (whether its 1 or 30 km thick), and second, it would be a shame to land on Europa’s surface a few meters from a sample and never be able to reach it.

We have devised one fireproof method of keeping alien worlds from being contaminated with Earth life: Cut the space program budgets.

As for detecting Europan aquatic life from space, has anyone been able to determine what that brown material is wherever we seen lines and impact areas on the surface ice? Freeman Dyson mentioned that Europan organic remains might even be in space around the moon and Jovian system from big enough celestial impacts that threw debris into space.

Unless humanity stupidly cuts itself off from space due to a continued misappropriation of funds or the highly mistaken belief that not focusing on space will somehow channel all that money into helping people, creatures from Earth will eventually “contaminate” the Sol system and beyond. However, so long as we are cautious and thorough, we should be able to keep our neighboring worlds pristine long enough to determine if they have their own creatures. Because let’s face it, there won’t be any human colonies or even science stations out there for decades as things are going now. Most of the work will still be done by robots.

“Eliminating contamination at Europa should be relatively easy – wave the drill/sampling device around for a few hours and let the radiation in the environment (from Jupiter) finish off any hardy Earth bugs.”

any idea how intense the radiation from Jupiter is ?
and
@andy
“Suppose we’re unlucky and somehow we manage to end up with a bunch of Deinococcus radiodurans on the probe. How would they fare in Jupiter’s radiation environment?”

is there a maximum limit of radiation that Deinococcus radiodurans can take?

If this gives you any idea, the Europa Orbiter envisioned by NASA last decade was expected to last only a month in Jupiter space once it got there due to the massive amounts of radiation from that planet. And the Galileo probe was regularly knocked into safe mode by all the radiation it received during its time in Jovian orbit.

Just what is the bacterial flux emanating from Earth due to the solar wind and radiation pressure on bacteria in the upper atmosphere?? This might indicate the rate of bacteria entering Europa’s gravity well and hence the probability of contamination from Earth.

I wonder if the risk of contamination is really all that great. Europan environments would not be much like those Earth environments where spacecraft are made — deep-sea vent (black smoker or cold seep) microorganisms, or perhaps those of the abyssal plain, might be able to survive in Europa’s seas… but spacecraft are not built on abyssal plains or in deep-sea vents, and I do not see how such organisms could get into spacecraft.

Organisms found on spacecraft will be common airborne bacteria, likely human-associated ones (like the questionable reports of Streptococcus mitis on Surveyor 3) — and it does not seem at all clear how such would survive in the Europan ocean.

Earth bacteria are part of an ecosystem; most would not survive well in an otherwise lifeless environment: or, possibly, in a totally alien ecosystem. Arguably invasive species ARE the problem they are on Earth precisely because the two ecosystems are not different enough: they can eat the same things, and thus compete for resources.

Care should be taken — but I do not think the chance of survival is nearly as great as is often thought.

Bill you have a wonderful point about Deinococcus radiodurans. It is my understanding that all the tests done on this hardy have been on how much radiation it can take in one burst. If these types of bacteria go into stringent mode, much of their remaining energy is focused into DNA repair, so the textbook answer to how much radiation it can take is very misleading in chronic situations.

“Eliminating contamination at Europa should be relatively easy – wave the drill/sampling device around for a few hours and let the radiation in the environment (from Jupiter) finish off any hardy Earth bugs.”

any idea how intense the radiation from Jupiter is ?
( that is, what is the radiation level in rems or whaterver unit?)

and
@andy
“Suppose we’re unlucky and somehow we manage to end up with a bunch of Deinococcus radiodurans on the probe. How would they fare in Jupiter’s radiation environment?”

is there a maximum limit of radiation that Deinococcus radiodurans can take?
( what is the radiation level in rems or whatever unit Deinococcus radiodurans can take?)

“Just what is the bacterial flux emanating from Earth due to the solar wind and radiation pressure on bacteria in the upper atmosphere?? This might indicate the rate of bacteria entering Europa’s gravity well and hence the probability of contamination from Earth.”

The Genesis and Stardust probes collected solar and cometary particles using that amazing aerogel stuff while in deep space. Did they also collect other matter during their missions, including microorganisms lifted from Earth’s upper atmosphere? Even if they were all dead, any good professional scientist in the appropriate fields should be able to identify organic remains.

This may be a good way to find out just how much living terrestrial matter is spread about the Sol system – and from anywhere else for that matter. Tell me there are some real scientists brave enough to conduct such a search.

“It was only when the oxygen atmosphere was in place and usable as a resource that multicellular life became successful enough to be a genuine long term survival advantage.”

this is only partially true. While multicellular life did develop when earths atmosphere became rich in oxygen that did not directly induce the jump to multicellularity. the rise in atmospheric oxygen levels allowed higher levels of oxygen to dissolve into the oceans. it was the rise in oceanic oxygen levels, not the rise in atmospheric oxygen levels that allowed complex life to develop. It is believed that Europa, despite having an incredibly thin oxygen atmosphere, maintains oceanic oxygen levels substantially higher the earth. Maybe Europan fish swim the oceans of the jovian moon after all

Astrobiologists have reproduced the conditions on the surface of Europa and found that some extremophiles survive

kfc 10/03/2011

A couple of weeks of ago, we looked at a study indicating that in Earth ejecta is more likely to end up in the Jovian system than on Mars, at least in some scenarios. That raised the possibility that life from Earth could have made its way to places like the Jovian moon Europa, which astronomers believe has a large salt water ocean beneath its icy crust.

But this would only possible if terrestrial bugs can survive the intense vacuum and radiation in interplanetary space. Astrobiologists have studied the way many creatures survive in a space-like conditions. They’ve looked at bacteria, fungi, viruses and even biomolecules such as DNA. Some lucky bugs have even survived the journey to the Moon and back.

But one branch of life has been largely ignored in these tests–archae. That’s surprising since these bacteria-like bugs often flourish in extreme conditions on Earth.

Today, Ximena Abrevaya at the Universidad de Buenos Aires in Argentina and a few pals go some way to righting this wrong. These guys created a vacuum similar to that which exists on the surface of Europa. They then placed three organisms in it: the salt-loving archae Natrialba magadii and Haloferax volcanii and the radiation-resistant bacteria Deinococcus radiodurans.

They then bombarded these creatures with the levels of ultraviolet radiation that might occur on the surface of Europa and waited to see what happened. None of Haloferax volcanii survived. But small amounts of both Natrialba magadii and Deinococcus radiodurans did.

That’s interesting because Deinococcus radiodurans is well known as one of the hardiest organisms on the planet. Numerous experiments have shown that it can survive levels of radiation, vacuum, acidity, cold and dehydration that would kill almost everything else.

For that reason, Deinococcus radiodurans has always been a candidate for seeding life elsewhere in the Solar System.

But now it looks as if it would have a companion on such a journey in the form of Natrialba magadii, an organism only isolated from the salty waters of Lake Magadi in Kenya in 1984.

Before getting too excited, however, it’s important to note that these experiments have a weakness: the tests lasted only for three hours.

That’s not long compared to interplanetary journey times: Earth ejecta takes tens of thousands of years to reach other bodies. However, the journey on a spacecraft from Earth would be much shorter, just a few years.

So if Abrevaya and co’s experiment tells us anything, it’s the importance of sterilising spacecraft before they leave here.

It’s just possible that right now, small colonies of Deinococcus radiodurans and Natrialba magadii are flourishing in the weak sunshine and cool wind around Viking 1 and 2.

When Biospheres Collide: A History of NASA’s Planetary Protection Programs (NASA SP-2011-4234) by Michael Meltzer.

This book presents the history of planetary protection by tracing the responses to the above concerns on NASA’s missions to the Moon, Mars, Venus, Jupiter, Saturn, and many smaller bodies of our solar system.

The book relates the extensive efforts put forth by NASA to plan operations and prepare space vehicles that return exemplary science without contaminating the biospheres of other worlds or our own.

To protect irreplaceable environments, NASA has committed to conducting space exploration in a manner that is protective of the bodies visited, as well as of our own planet.

GPO price hardcover $57.00, GPO price paperback $49.00. Other commercial vendors such as Amazon.com are also expected to sell this book.

Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last nine years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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